With Borderlands 3 (opens in new tab) just over a week away from its Steam debut, publisher 2K Games has posted an FAQ (opens in new tab) breaking down all there is to know about it, including how crossplay will work, how to transfer saves, and when exactly the Steam version will unlock.
Borderlands 3 on both Steam and the Epic Games Store (after an update) will have a PC Crossplay screen that will enable the feature to be either enabled or disabled. Either way, you'll also be prompted to select a crossplay display name that will be used for the new "Shift Matchmaking" functionality. Your display name and crossplay selection can both be changed whenever you like from the Options menu. Crossplay with console versions of the game is not supported "at this time."
Saved games can be moved, if you've been playing on one platform and would like to switch to the other, but you'll have to do so manually. Detailed instructions on doing so will be posted by the time the Steam version hits, but 2K warned that "you run the risk of potentially losing your save files," so back your stuff up first. In-game mail exchanges will be restricted to players on the same platform at release, but a patch enabling cross-platform mail is planned for the near future.
Transferring achievements sounds like a trickier proposition. "If you're transferring an existing Epic Save file to your Steam account, be aware that you will not immediately receive Steam Achievements you may have already earned with that save file," the FAQ states. "Certain Steam Achievements may still be earned on that character based on completing the requisite criteria again, but at this time, we can't guarantee that Steam will register these Achievements consistently. All Steam Achievements can be earned with any new characters you create on Steam."
Borderlands 3 preloading on Steam (opens in new tab) will begin in the early afternoon (PT) on March 10. It's not in the FAQ, but 2K said that it will unlock at 7 am PDT/10 am EDT/2pm GMT on March 13.
Update: 2K has clarified that the Steam FAQ is incorrect: Borderlands will unlock on Steam at 7 am PDT, not PST, which works out to 2 pm GMT. I've updated the unlock times in the post.